Optical emission spectroscopy (oes) for remote plasma monitoring

ABSTRACT

Methods and systems for etching substrates using a remote plasma are described. Remotely excited etchants are formed in a remote plasma and flowed through a showerhead into a substrate processing region to etch the substrate. Optical emission spectra are acquired from the substrate processing region just above the substrate. The optical emission spectra may be used to determine an endpoint of the etch, determine the etch rate or otherwise characterize the etch process. A weak plasma may be present in the substrate processing region. The weak plasma may have much lower intensity than the remote plasma. In cases where no bias plasma is used above the substrate in an etch process, a weak plasma may be ignited near a viewport disposed near the side of the substrate processing region to characterize the etchants.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 15/484,985 filed Apr. 11, 2017, the entire contents of whichare hereby incorporated by reference in their entirety for all purposes.

FIELD

Embodiments disclosed herein relate to remote plasma etch processes.

BACKGROUND

Integrated circuits are made possible by processes which produceintricately patterned material layers on substrate surfaces. Producingpatterned material on a substrate requires controlled methods forremoval of exposed material. Chemical etching is used for a variety ofpurposes including transferring a photoresist pattern into underlyinglayers, thinning layers or thinning lateral dimensions of featuresalready present on the surface. Often it is desirable to have an etchprocess which etches one material faster than another helping e.g. apattern transfer process proceed. Such an etch process is said to beselective of the first material relative to the second material. As aresult of the diversity of materials, circuits and processes, etchprocesses have been developed with a selectivity towards a variety ofmaterials.

Dry etch processes are often desirable for selectively removing materialfrom semiconductor substrates. The desirability stems from the abilityto gently remove material from miniature structures with minimalphysical disturbance. Dry etch processes also allow the etch rate to beabruptly stopped by removing the gas phase reagents. Some dry-etchprocesses involve the exposure of a substrate to remote plasmaby-products formed from one or more precursors. Remote excitation ofetchants in a remote plasma system (instead of locally) may desirablyincrease selectivity.

Methods and systems are needed to monitor aspects of remote plasmasin-situ for a variety of purposes.

SUMMARY

Methods and systems for etching substrates using a remote plasma aredescribed. Remotely excited etchants are formed in a remote plasma andflowed through a showerhead into a substrate processing region to etchthe substrate. Optical emission spectra are acquired from the substrateprocessing region just above the substrate. The optical emission spectramay be used to determine an endpoint of the etch, determine the etchrate or otherwise characterize the etch process in-situ. A weak plasmamay be present in the substrate processing region. The weak plasma mayhave lower intensity than the remote plasma. In cases where no biasplasma above the substrate is used in an etch process, a weak plasma maybe ignited near a viewport disposed near the side of the substrateprocessing region to characterize the etchants.

Embodiments disclosed herein include methods of etching a substrate. Themethods include placing the substrate in a substrate processing regionof a substrate processing chamber. The methods further include flowing afluorine-containing precursor into a remote plasma region separated fromthe substrate processing region by a showerhead. The methods furtherinclude forming a remote plasma having a remote plasma power in theremote plasma region. The methods further include producing plasmaeffluents from the fluorine-containing precursor in the remote plasma inthe remote plasma region. The methods further include flowing the plasmaeffluents through the showerhead into the substrate processing region.The methods further include etching the substrate with the plasmaeffluents. The methods further include forming a local plasma having alocal plasma power in the substrate processing region. The methodsfurther include acquiring an optical emission spectrum through aviewport affixed to a side of the substrate processing chamber, the sideforming a border of the substrate processing region. The opticalemission spectrum represents intensity as a function of opticalwavelength and the optical emission spectrum is acquired with an opticalemission spectrometer.

The remote plasma power of the remote plasma may exceed the local plasmapower of the local plasma by a factor of ten or more. The local plasmamay be centered over the substrate. The local plasma may be positionedabove the substrate and outside an edge of the substrate near theviewport. The local plasma may be formed using an electrode located onthe outside of the viewport and the local plasma power may be appliedbetween the electrode and the substrate processing chamber. The localplasma may be formed using a first electrode and a second electrode,each positioned on the outside of the viewport and the local plasmapower may be applied between the first electrode and the secondelectrode.

Embodiments disclosed herein include substrate processing chambers Thesubstrate processing chambers include a remote plasma region. The remoteplasma region is configured to receive a fluorine-containing precursorand form a remote plasma from the fluorine-containing precursor. Thesubstrate processing chambers further include a remote plasma powersupply configured to apply a remote plasma power to the remote plasmaregion and configured to form the remote plasma. The substrateprocessing chambers further include a substrate processing region. Thesubstrate processing chambers further include a showerhead positionedbetween the remote plasma region and the substrate processing region.The substrate processing region is fluidly coupled to the remote plasmaregion by through-holes in the showerhead. The substrate processingchambers further include a pedestal configured to support a substrate.The substrate processing chambers further include a flange attached tothe substrate processing chamber. The flange forms a vacuum seal withthe substrate processing chamber. The substrate processing chamberfurther includes a viewport attached to the flange forming a vacuum sealwith the flange. The viewport is optically transmissive in a nearinfrared spectrum. The substrate processing chambers further include anoptical emission spectrometer configured to receive optical radiationafter the optical radiation passes through the viewport. The opticalemission spectrometer is positioned on an exterior of the viewport andthe optical radiation originates from inside the substrate processingregion above the substrate.

The substrate processing chambers may further include a local plasmapower supply configured to form a local plasma in the substrateprocessing region. The local plasma may have a local plasma power lessthan 10% of the remote plasma power. The substrate processing chambersmay further include a fiber optic cable configured to guide the opticalradiation from the viewport to the optical emission spectrometer. Thesubstrate processing chambers may further include an electrode proximalto the viewport. The electrode may be positioned on the exterior of theviewport. The substrate processing chambers may further include a plasmapower supply configured to apply a plasma power to the electrode. Thesubstrate processing chambers may further include a second electrodeconfigured to apply a plasma power to the electrode. The electrode maybe electrically insulated from the second electrode.

Embodiments disclosed herein include optical emission spectrometerassemblies. The optical emission spectrometer assemblies include aflange configured to attach to a substrate processing chamber. Theflange is configured to form a vacuum seal with the substrate processingchamber. The optical emission spectrometer assemblies further include aplanar viewport attached to the flange forming a vacuum seal with theflange. The planar viewport is optically transmissive in a near infraredspectrum. The optical emission spectrometer assemblies further includean electrode proximal to the planar viewport. The electrode is disposedon an external side of the planar viewport. The optical emissionspectrometer assemblies further include an optical emission spectrometerconfigured to receive optical radiation after the optical radiationpasses through the planar viewport. The optical emission spectrometer ispositioned on the external side of the planar viewport. The opticalemission spectrometer assemblies further include a plasma power supplyconfigured to apply a plasma power to the electrode.

The optical emission spectrometer assemblies may further include a fiberoptic cable configured to guide infrared light from the planar viewportto the optical emission spectrometer. The plasma power supply may beconfigured to apply the plasma power between the electrode and thesubstrate processing chamber. The optical emission spectrometerassemblies may further include a second electrode proximal to the planarviewport. The electrode may be electrically insulated from the secondelectrode. The plasma power supply may be configured to apply the plasmapower between the electrode and the second electrode.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the disclosed embodiments. The features andadvantages of the disclosed embodiments may be realized and attained bymeans of the instrumentalities, combinations, and methods described inthe specification.

DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the embodimentsmay be realized by reference to the remaining portions of thespecification and the drawings.

FIG. 1 shows a schematic cross-sectional view of a substrate processingchamber according to embodiments.

FIG. 2 is a flow chart of a remote plasma etch process according toembodiments.

FIG. 3A shows a schematic cross-sectional view of a substrate processingchamber according to embodiments.

FIG. 3B shows a schematic cross-sectional view of a substrate processingchamber according to embodiments.

FIG. 4 is an optical emission spectrum according to embodiments.

FIG. 5 is a plot of etch amount correlation with fluorine signalaccording to embodiments.

FIG. 6A shows a cross-sectional side view of a weak plasma viewportaccording to embodiments.

FIG. 6B shows a cross-sectional end view of a weak plasma viewportaccording to embodiments.

FIG. 7A shows a cross-sectional side view of a weak plasma viewportaccording to embodiments.

FIG. 7B shows a cross-sectional end view of a weak plasma viewportaccording to embodiments.

FIG. 7C shows a cross-sectional side view of a weak plasma viewportaccording to embodiments.

FIG. 8A shows a cross-sectional side view of a weak plasma viewportaccording to embodiments.

FIG. 8B shows a cross-sectional side view of a weak plasma viewportaccording to embodiments.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

Methods and systems for etching substrates using a remote plasma aredescribed. Remotely excited etchants are formed in a remote plasma andflowed through a showerhead into a substrate processing region to etchthe substrate. Optical emission spectra are acquired from the substrateprocessing region just above the substrate. The optical emission spectramay be used to determine an endpoint of the etch, determine the etchrate or otherwise characterize the etch process in-situ. A weak plasmamay be present in the substrate processing region. The weak plasma mayhave much lower intensity than the remote plasma. In cases where no biasplasma above the substrate is used in an etch process, a weak plasma maybe ignited near a viewport disposed near the side of the substrateprocessing region to characterize the etchants.

In the past, gas phase etch processes have excited NF₃ in a local plasmainside substrate processing region. Optical emission spectroscopy wasperformed by flowing some of the reactants in the substrate processingregion through tubing to a separate plasma used for the characterizationand then disposing any chemical effluents through a vacuum pump.Recently, high selectivity gas-phase etch processes have been developedusing a spatially-constrained remote plasma region separated from thesubstrate processing region by a showerhead (sometimes a dual-channelshowerhead). Plasma effluents are formed in the remote plasma region andflow into the substrate processing region through the showerhead. Theremote plasma effluents are optionally further excited in a bias plasmaabove the substrate.

The methods and systems described herein provide the benefit ofcharacterizing remote plasma etch processes in the substrate processingregion where there is more space than in the remote plasma region. Thecharacterization of the plasma effluents occurs closer to the substrate,providing a more accurate determination of the etch process compared tothe more circuitous sampling routes used previously.

FIG. 1 shows a schematic cross-sectional view of an exemplary substrateprocessing chamber. The schematic of the substrate processing chamber1001 serves to introduce the optical emission spectrometer but alsoprovide context for alternative configurations and details provided insubsequent descriptions. Later drawings will provide less detailcompared to FIG. 1 but only for the sake of brevity. Any combination offeatures found in FIG. 1 may be present in any or all subsequentembodiments. The substrate processing chamber 1001 has a remote plasmaregion 1015 and a substrate processing region 1033 inside. The remoteplasma region 1015 is partitioned from the substrate processing region1033 by an ion suppressor 1023 and a showerhead 1025.

A top plate 1017, ion suppressor 1023, showerhead 1025, and a substratesupport 1065 (also known as a pedestal), having a substrate 1055disposed thereon, are shown and may each be included according to allembodiments described herein. The pedestal 1065 may have a heat exchangechannel through which a heat exchange fluid flows to control thetemperature of the substrate 1055. This configuration may allow thesubstrate 1055 temperature to be cooled or heated to maintain relativelylow temperatures, such as between −20° C. to 200° C. The pedestal 1065may also be resistively heated to relatively high temperatures, such asbetween 100° C. and 1100° C., using an embedded heater element.

The etchant precursors flow from the etchant supply system 1010 throughthe holes in the top plate 1017 into the remote plasma region 1015. Thestructural features may include the selection of dimensions andcross-sectional geometries of the apertures in the top plate 1017 todeactivate back-streaming plasma in cases where a plasma is generated inremote plasma region 1015. The top plate 1017, or a conductive topportion of the substrate processing chamber 1001, and the showerhead1025 are shown with an intervening insulating ring 1020, which allows anAC potential to be applied to the top plate 1017 relative to theshowerhead 1025 and/or the ion suppressor 1023. The insulating ring 1020may be positioned between the top plate 1017 and the showerhead 1025and/or the ion suppressor 1023 enabling a capacitively-coupled plasma(CCP) to be formed in the remote plasma region 1015. The remote plasmaregion 1015 houses the remote plasma.

The plurality of holes in the ion suppressor 1023 may be configured tocontrol the passage of the activated gas, i.e., the ionic, radical,and/or neutral species, through the ion suppressor 1023. For example,the aspect ratio of the holes, or the hole diameter to length, and/orthe geometry of the holes may be selected so that the flow ofionically-charged species in the activated gas passing through the ionsuppressor 1023 is reduced. The holes in the ion suppressor 1023 mayinclude a tapered portion that faces the remote plasma region 1015, anda cylindrical portion that faces the showerhead 1025. The cylindricalportion may be shaped and dimensioned to control the flow of ionicspecies passing to and through the showerhead 1025. An adjustableelectrical bias may also be applied to the ion suppressor 1023 as anadditional means to control the flow of ionic species through thesuppressor. The ion suppressor 1023 may function to reduce or eliminatethe amount of ionically charged species traveling from the plasmageneration region to the substrate. Uncharged neutral and radicalspecies may still pass through the openings in the ion suppressor toreact with the substrate.

Remote plasma power can be of a variety of frequencies or a combinationof multiple frequencies. The remote plasma may be provided by remote RFpower delivered from the remote plasma power supply 1068 to the topplate 1017 relative to the ion suppressor 1023, relative to theshowerhead 1025, or relative to both the ion suppressor 1023 and theshowerhead 1025 (as shown). The remote RF power may be between 10 wattsand 10,000 watts, between 10 watts and 5,000 watts, preferably between25 watts and 2000 watts or more preferably between 50 watts and 1500watts to increase the longevity of chamber components. The remote RFfrequency applied in the exemplary processing system to the remoteplasma region may be low RF frequencies less than 200 kHz, higher RFfrequencies between 10 MHz and 15 MHz, or microwave frequencies greaterthan 1 GHz in embodiments. The plasma power may be capacitively-coupled(CCP) or inductively-coupled (ICP) into the remote plasma region.

Plasma effluents derived from the etchant precursors in the remoteplasma region 1015 may travel through apertures in the ion suppressor1023, and/or the showerhead 1025 and into the substrate processingregion 1033 through through-holes or the first fluid channels 1019 ofthe showerhead in embodiments. Little or no plasma may be present insubstrate processing region 1033 during the remote plasma etch process.The plasma effluents react with the substrate to etch material from thesubstrate.

The showerhead 1025 may be a dual channel showerhead (DCSH). The dualchannel showerhead 1025 may provide for etching processes that allow forseparation of etchants outside of the substrate processing region 1033to provide limited interaction with chamber components and each otherprior to being delivered into the substrate processing region 1033. Theshowerhead 1025 may comprise an upper plate 1014 and a lower plate 1016.The plates may be coupled with one another to define a volume 1018between the plates. The plate configuration may provide the first fluidchannels 1019 through the upper and lower plates, and the second fluidchannels 1021 through the lower plate 1016. The formed channels may beconfigured to provide fluid access from the volume 1018 through thelower plate 1016 via the second fluid channels 1021 alone, and the firstfluid channels 1019 may be fluidly isolated from the volume 1018 betweenthe plates and the second fluid channels 1021. The volume 1018 may befluidly accessible through a side of the showerhead 1025 and used tosupply an unexcited precursor in embodiments.

Optionally, a bias plasma power may be present in the substrateprocessing region in embodiments. The bias plasma may be used to furtherexcite plasma effluents already excited in the remote plasma. The biasplasma refers to a local plasma located just above the substrate. Theterm bias plasma is used since the plasma effluents may be ionizedand/or accelerated towards the substrate to beneficially accelerate orprovide incoming alignment to some etch processes. The bias plasma maybe formed by applying bias plasma power from a bias plasma power supply1069 to the substrate 1055/pedestal 1065 relative to the ion suppressor1023, relative to the showerhead 1025, or relative to both the ionsuppressor 1023 and the showerhead 1025 (as shown). The bias RF plasmapower may be lower than the remote RF power. The bias RF plasma powermay be below 20%, below 15%, below 10% or below 5% of the remote RFplasma power. The bias RF plasma power may be between 1 watt and 1,000watts, between 1 watt and 500 watts, or between 2 watts and 100 watts inembodiments. The bias RF plasma frequency applied in the exemplaryprocessing system to the remote plasma region may be low RF plasmafrequencies less than 200 kHz, higher RF plasma frequencies between 10MHz and 15 MHz, or microwave frequencies greater than 1 GHz inembodiments. The bias RF plasma frequency may be different from theremote RF frequency to further improve the integrity of the opticalemission spectra. The plasma power may be capacitively-coupled (CCP) orinductively-coupled (ICP) into the substrate plasma region.

A viewport 1071 is disposed on the side of the substrate processingchamber 1001 and forms a border of the substrate processing region 1033.The viewport 1071 transmits optical radiation and may be transmissive inthe infrared portion of the optical spectrum. Viewports described hereinmay be transmissive between 650 nm and 800 nm, between 680 nm and 760 nmor between 700 nm and 740 nm in embodiments. An optical emissionspectrometer (OES) is disposed outside the viewport 1071 and configuredto receive optical radiation, preferably infrared radiation, originatingfrom the bias plasma formed in the substrate processing region 1033. Incases where there is no bias plasma, a weak plasma may be formed on theinterior side of the viewport 1071 to facilitate the acquisition of theoptical emission spectrum by the optical emission spectrometer. Thecharacteristics of the weak plasma (power, frequency) may be the same asthe bias power properties provided earlier, according to embodiments.For example, the weak RF plasma power may be below 20%, below 15%, below10% or below 5% of the remote RF plasma power. The weak RF plasma powermay be between 1 watt and 1,000 watts, between 1 watt and 500 watts, orbetween 2 watts and 100 watts in embodiments. The weak RF plasmafrequency applied in the exemplary processing system to the remoteplasma region may be low RF plasma frequencies less than 200 kHz, higherRF plasma frequencies between 10 MHz and 15 MHz, or microwavefrequencies greater than 1 GHz in embodiments. The weak RF plasmafrequency may be different from the remote RF frequency to furtherimprove the integrity of the optical emission spectra. The weak plasmapower may be capacitively-coupled (CCP) or inductively-coupled (ICP)into the substrate plasma region.

To better understand and appreciate the embodiments disclosed herein,reference is now made to FIG. 2 which is a flow chart of a highlyselective etch process 2010 according to embodiments. Prior to the firstoperation, the substrate is patterned and then placed within thesubstrate processing region in optional operation 2100. Afluorine-containing precursor (e.g. NF₃) may be flowed into the remoteplasma region in operation 2200. A remote plasma is formed from thefluorine-containing precursor in the remote plasma region by applying aremote plasma power across the remote plasma region to form plasmaeffluents. The plasma effluents are flowed through a showerhead disposedbetween the remote plasma region and the substrate processing region inoperation 2300. The plasma effluents flow through the showerhead fromthe remote plasma region into the substrate processing region. A biasplasma is formed by applying a bias plasma power across the substrateprocessing region to further excite the plasma effluents in operation2400. The bias plasma power is less than the remote plasma power and thebias plasma may be referred to as a “weak” plasma in embodiments.Portions of a patterned substrate are selectively etched in operation2500. An optical emission spectrum is acquired through a viewport in theside of the substrate processing chamber (operation 2600) and the etchis stopped based on the results. The viewport forms a border of thesubstrate processing region. Optionally, the patterned substrate isremoved from the substrate processing region (operation 2700).

FIG. 3A shows a schematic cross-sectional view of an exemplary substrateprocessing chamber. Process and equipment parameters given earlier applyto all embodiments described herein. Similarly, process and equipmentparameters given here and in subsequent discussions may be used for allother embodiments described herein. The substrate processing chamber3001 has a remote plasma region 3015 and a substrate processing region3033 inside. The remote plasma region 3015 is partitioned from thesubstrate processing region 3033 by a showerhead 3025 with through-holes3019 configured to pass plasma effluents.

A top plate 3017, showerhead 3025, and a pedestal 3065 supporting asubstrate 3055 are shown. A fluorine-containing precursor may flow fromthe etchant supply system 3010 into the remote plasma region 3015. Thetop plate 3017 and the showerhead 3025 are electrically-separatedconductors separated by insulating ring 3020. An AC potential (theremote plasma power) is applied to the top plate 3017 relative to theshowerhead 3025 to form the remote plasma. The remote plasma may be acapacitively-coupled plasma (CCP) in the remote plasma region 3015.Plasma frequencies and plasma powers provided by a remote plasma powersupply (not shown) were provided previously.

Plasma effluents derived from the fluorine precursors in the remoteplasma region 3015 may travel through the through-holes 3019 in theshowerhead 3025 and into the substrate processing region 3033. A biasplasma power is applied by a bias plasma power supply (not shown) to thesubstrate processing region 3033. The bias plasma further excites theplasma effluents. The bias plasma weakly ionizes and accelerates plasmaeffluents towards the substrate to beneficially accelerate or provideincoming alignment to the etch processes. The bias plasma may be formedby applying bias plasma power from a bias plasma power supply to thesubstrate 3055/pedestal 3065 relative to the showerhead 3025. The plasmaeffluents react with the substrate to etch material from the substrate.

Acquisition of optical emission spectra uses the recombination ofelectrons with ions to emit photons indicative of a presence of specificatomic species. In the embodiment represented in FIG. 3A, the biasplasma is sufficient to supply the ionization needed to acquire anoptical emission spectrum. To further enable the measurement, a viewport3071 is disposed in the side of the substrate processing chamber 3001.The optical emission spectrum is measured using an optical emissionspectrometer on the outside of the viewport 3071.

FIG. 3B shows a schematic cross-sectional view of an exemplary substrateprocessing chamber. The substrate processing chamber 3001 has a remoteplasma region 3015 and a substrate processing region 3033 inside. Theremote plasma region 3015 is partitioned from the substrate processingregion 3033 by a showerhead 3025 with through-holes 3019 to pass plasmaeffluents. A top plate 3017, showerhead 3025, and a pedestal 3065supporting a substrate 3055 are shown. A fluorine-containing precursormay flow from the etchant supply system 3010 into the remote plasmaregion 3015. An AC potential (the remote plasma power) is applied to thetop plate 3017 relative to the showerhead 3025 to form the remoteplasma.

Plasma effluents derived from the fluorine precursors in the remoteplasma region 3015 travel through the through-holes 3019 in theshowerhead 3025 and into the substrate processing region 3033. Theplasma effluents react with the substrate to etch material from thesubstrate.

No bias plasma power is applied to the substrate processing region 3033in embodiments. The substrate processing region 3033 may be referred toas plasma-free and may be devoid of plasma in embodiments. A weak plasmanear the substrate processing region is used to obtain an opticalemission spectrum. The weak plasma results in recombination of electronswith ions and concomitant emission of photons indicative of a presenceof specific atomic species. Therefore a weak plasma is formed just onthe inside of a viewport 3071 by a variety of techniques to be describedherein. The viewport 3071 is disposed in the side of the substrateprocessing chamber 3001. The optical emission spectrum is measured usingan optical emission spectrometer on the outside of the viewport 3071.The weak plasma is formed by applying weak plasma power from a weakplasma power supply to one or more electrode(s) (not shown) near theviewport 3071. The weak RF plasma power may be lower than the remote RFpower. A relatively low weak RF plasma power avoids swamping the remoteplasma OES signal with characteristics of the weak local plasma. Theweak RF plasma power may be below 10%, below 8%, below 5% or below 3% ofthe remote RF plasma power. The weak RF plasma power may be between 0.1watts and 300 watts, between 0.2 watts and 100 watts, or between 0.5watts and 20 watts in embodiments. The weak RF plasma frequency appliedin the exemplary processing system to the remote plasma region may below RF plasma frequencies less than 200 kHz, higher RF plasmafrequencies between 10 MHz and 15 MHz, or microwave frequencies greaterthan 1 GHz in embodiments. The weak RF plasma frequency may be differentfrom the remote RF frequency to further improve the integrity of theoptical emission spectra. For example, the weak RF plasma frequency maybe 60 kHz and the remote RF frequency may be 13 MHz. The plasma powermay be capacitively-coupled (CCP) or inductively-coupled (ICP) into thesubstrate plasma region.

The pressure in the substrate processing region and the remote plasmaregion during the etching operations may be between 0.01 Torr and 50Torr, between 0.1 Torr and 15 Torr or between 0.5 Torr and 10 Torr inembodiments. The temperature of the patterned substrate during theetching operations may be between −20° C. and 450° C., between 0° C. and350° C. or between 5° C. and 200° C. in embodiments.

Reference is now made to FIG. 4 which is plot of an optical emissionspectra. An optical emission spectrum 4010 is depicted which representsa concurrent remote plasma and a weak local plasma. Another opticalemission spectrum 4020 is depicted which represents only a weak localplasma. The peaks near 703.7 nm, 712.8 nm, and 720.2 nm correspond withfluorine atom concentration. The peaks near 706.5 nm and 728.1 nmcorrespond with helium atom concentration. Helium or another inert gasmay be used to benefit the etch process but may also be useful tocompare and normalize the fluorine peaks. Qualitatively, the fluorinemeasurements can be seen to become more pronounced when the remoteplasma is in use. More generally, the fluorine measurements may be usedto determine whether the fluorine concentration is changing, has reacheda plateau, or has reached a predetermined setpoint during an etchprocess.

FIG. 5 is a plot of etch amount correlation with fluorine signalaccording to embodiments. The fluorine signal normalized to heliumsignal is shown on the x-axis whereas the etch amount corresponds to they-axis. A plot of etch amount (proportion to etch rate) versusnormalized fluorine signal 5010 is shown to be roughly linear with anoffset. The linearity enables the normalized fluorine signal to be anin-situ indicator of the etch rate of a substrate without measuring thesubstrate directly.

FIGS. 6A and 6B show cross-sectional side views of a weak plasmaviewport according to embodiments. FIG. 6A shows a substrate processingregion 6033 with a tubular viewport 6071 affixed to the side and forminga vacuum seal with the wall of the substrate processing chamber. A firstelectrode 6072-1 and a second electrode 6072-2 are affixed to thetubular viewport 6071 on opposite sides. All electrodes described hereinmay be copper adhesive tape or silver paste to facilitate attaching theelectrodes to the various viewports according to embodiments. Otheradhesive formats may also be used. Alternatively, the electrodes maysimply be placed near the tubular viewport 6071 on opposite sides sincemechanical contact between the viewport and the electrodes is notnecessary to form the plasma. A weak plasma 6034 is formed on the insideof the tubular viewport 6071 by applying a weak RF plasma power from aweak RF plasma power supply (not shown) between the first electrode6072-1 and the second electrode 6072-2. FIG. 6B shows an end view of thesame configuration and includes a view of the weak plasma power supply6068. A fiber optic cable 6073 is configured to guide optical radiationfrom the weak plasma 6034 through the tubular viewport 6071 and into theoptical emission spectrometer 6070.

FIGS. 7A, 7B, and 7C show cross-sectional side views of a weak plasmaviewport according to embodiments. FIG. 7A shows a substrate processingregion 7033 with a tubular viewport 7071 affixed to the side and forminga vacuum seal with the wall of the substrate processing chamber. Anelectrode 7072-1 is affixed to the tubular viewport 7071 around theexterior of the tubular viewport 7071. The electrode 7072-1 may be apiece of conducting adhesive tape (e.g. copper) or a layer of conductivepaste (e.g. silver) to facilitate attaching the electrode 7072-1 to thetubular viewport 7071 according to embodiments. The electrode 7072-1 maysimply be a conducting hoop looped loosely around the tubular viewport7071 since forming the weak plasma does not rely on mechanical contactbetween the tubular viewport 7071 and the electrode 7072-1. A weakplasma 7034-1 is formed on the inside of the tubular viewport 7071 byapplying a weak RF plasma power from a weak RF plasma power supply7068-1 between the electrode 7072-1 and the rest of the substrateprocessing chamber or the wall shown as a border of the substrateprocessing region 7033. Also shown is a fiber optic cable 7073configured to guide optical radiation from the weak plasma 7034 throughthe tubular viewport 7071 and into the optical emission spectrometer7070. FIG. 7B shows an end view of the same configuration and includes aview of the electrode 7072-1 which is shaped like a hoop. FIG. 7C showsa related configuration having an electrode 7072-2 over the end of thetubular viewport 7071 and the fiber optic cable 7073 is relocated topeer at the weak plasma 7034-2 from a different angle through anunobstructed portion of the tubular viewport 7071. A weak RF plasmapower supply 7068-2 provides the weak RF plasma power between theelectrode 7072-2 and the wall of the substrate processing chamber.

FIGS. 8A and 8B show cross-sectional side views of a weak plasmaviewport according to embodiments. FIG. 8A shows a substrate processingregion 8033 with a planar viewport 8071 affixed to the side and forminga vacuum seal with the wall of the substrate processing chamber. A firstelectrode 8072-1 and a second electrode 8072-2 are affixed to the planarviewport 8071 without any direct electrical connection between them. Thefirst electrode 8072-1 and the second electrode may be pieces ofconducting adhesive tape (e.g. copper), a layer of conductive paste(e.g. silver) or electrodes placed near or adjacent to the planarviewport 8071. The electrodes (8072-1, 8072-2) do not need to be inmechanical contact with the planar viewport 8071, in embodiments, toprovide the capability of forming a weak plasma 8034-1. The weak plasma8034-1 is formed on the inside of the planar viewport 8071 by applying aweak RF plasma power from a weak RF plasma power supply 8068-1 betweenthe first electrode 8072-1 and the second electrode 8072-2. Also shownis a fiber optic cable 8073 configured to guide optical radiation fromthe weak plasma 8034-1 through the planar viewport 8071 and into theoptical emission spectrometer 8070. FIG. 8B shows a substrate processingregion 8033 with a planar viewport 8071 affixed to the side and forminga vacuum seal with the wall of the substrate processing chamber. Anelectrode 8072-3 is affixed to the planar viewport 8071. The firstelectrode 8072-1 may again be a piece of conducting adhesive tape, alayer of conductive paste, or an electrode placed very near orcontacting the planar viewport 8071. The weak plasma 8034-1 is formed onthe inside of the planar viewport 8071 by applying a weak RF plasmapower from a weak RF plasma power supply 8068-2 between the electrode8072-3 and the rest of the substrate processing chamber or the wallshown as a border of the substrate processing region 8033. Also shown isa fiber optic cable 8073 configured to guide optical radiation from theweak plasma 8034-2 through the planar viewport 8071 and into the opticalemission spectrometer 8070.

The tubular viewports described herein may be more prone to breakagesince they stick out from the substrate processing chamber. The planarviewports provide the benefit of reducing the chance of accidentallybreaking the viewport. The thickness of the planar viewports describedherein affect the intensity of the weak plasmas inside the substrateprocessing chamber near the substrate. The thickness of the planarviewports may be between 1 mm and 15 mm, between 2 mm and 10 mm orpreferably between 3 mm and 8 mm according to embodiments. The heightand/or width of the planar viewports (as viewed from the axis of thethinnest dimension) may be between 20 mm and 100 mm or between 30 mm and70 mm in embodiments. The fiber optic cable in all embodiments describedherein may be positioned to the side of the substrate and just above themajor plane of the substrate to preferentially sample the portion of theplasma effluents most likely to be participating in the etch process.The fiber optic cable may point horizontally (parallel to the majorplane of the substrate) between 1 mm and 10 mm above the top surface ofthe substrate according to embodiments.

In embodiments, an ion suppressor (which may be the showerhead) may beused to provide radical and/or neutral species for gas-phase etching.The ion suppressor may also be referred to as an ion suppression elementand may be positioned between the remote chamber region and thesubstrate processing region along with the showerhead. In embodiments,for example, the ion suppressor is used to filter etching plasmaeffluents en route from the remote plasma region(s) to the substrateprocessing region. The ion suppressor may be used to provide a reactivegas having a higher concentration of radicals than ions. Plasmaeffluents pass through the ion suppressor disposed between the remoteplasma region and the substrate processing region. The ion suppressorfunctions to dramatically reduce or substantially eliminate ionicspecies traveling from the plasma generation region to the substrate.The ion suppressors described herein are simply one way to achieve a lowelectron temperature in the substrate processing region during thegas-phase etch processes described herein.

In embodiments, an electron beam is passed through the substrateprocessing region in a plane parallel to the substrate to reduce theelectron temperature of the plasma effluents. A simpler showerhead maybe used if an electron beam is applied in this manner. The electron beammay be passed as a laminar sheet disposed above the substrate inembodiments. The electron beam provides a source of neutralizingnegative charge and provides a more active means for reducing the flowof positively charged ions towards the substrate and increasing the etchselectivity in embodiments. The flow of plasma effluents and variousparameters governing the operation of the electron beam may be adjustedto lower the electron temperature measured in the substrate processingregion.

The electron temperature may be measured using a Langmuir probe in thesubstrate processing region during excitation of a plasma in the remoteplasma. In all plasma-free regions described herein (especially in thesubstrate processing region), the electron temperature may be less than0.5 eV, less than 0.45 eV, less than 0.4 eV, or less than 0.35 eV. Theseextremely low values for the electron temperature are enabled by thepresence of the electron beam, showerhead and/or the ion suppressor.Uncharged neutral and radical species may pass through the electron beamand/or the openings in the ion suppressor to react at the substrate.Such a process using radicals and other neutral species can reduceplasma damage compared to conventional plasma etch processes thatinclude sputtering and bombardment. Embodiments disclosed herein arealso advantageous over conventional wet etch processes where surfacetension of liquids can cause bending and peeling of small features.

The substrate processing region may be described herein as “plasma-free”during the etch processes described herein. “Plasma-free” does notnecessarily mean the region is devoid of plasma. A weak plasma may bepresent to perform the optical emission spectroscopy measurement but theregion directly above the substrate may be devoid of plasma since theweak plasma is positioned off to the side of the substrate processingregion in embodiments. Ionized species and free electrons created withinthe plasma region may travel through pores (apertures) in the partition(showerhead) at exceedingly small concentrations. The borders of theplasma in the remote plasma region (e.g. the remote chamber regionand/or the remote plasma region) may encroach to some small degree uponthe substrate processing region through the apertures in the showerhead.Furthermore, a low intensity plasma may be created in the substrateprocessing region without eliminating desirable features of the etchprocesses described herein. All causes for a plasma having much lowerintensity ion density than the remote plasma region during the creationof the excited plasma effluents do not deviate from the scope of“plasma-free” as used herein.

As used herein “substrate” may be a support substrate with or withoutlayers formed thereon. The patterned substrate may be an insulator or asemiconductor of a variety of doping concentrations and profiles andmay, for example, be a semiconductor substrate of the type used in themanufacture of integrated circuits. Exposed “silicon oxide” of thepatterned substrate is predominantly SiO₂ but may include concentrationsof other elemental constituents such as, e.g., nitrogen, hydrogen andcarbon. In some embodiments, silicon oxide portions etched using themethods disclosed herein consist essentially of silicon and oxygen.Exposed “silicon nitride” of the patterned substrate is predominantlySi₃N₄ but may include concentrations of other elemental constituentssuch as, e.g., oxygen, hydrogen and carbon. In some embodiments, siliconnitride portions described herein consist essentially of silicon andnitrogen. Generally speaking, a first exposed portion of a patternedsubstrate is etched faster than a second exposed portion. The firstexposed portion may have an atomic stoichiometry which differs from thesecond exposed portion. In embodiments, the first exposed portion maycontain an element which is not present in the second exposed portion.Similarly, the second exposed portion may contain an element which isnot present in the first exposed portion according to embodiments.

The term “precursor” is used to refer to any chemical which takes partin a reaction to either remove material from or deposit material onto asurface. “Plasma effluents” describe gas exiting from the remote plasmaregion and entering the remote chamber region and/or the substrateprocessing region. Plasma effluents are in an “excited state” wherein atleast some of the gas molecules are in vibrationally-excited,dissociated and/or ionized states. A “radical precursor” is used todescribe plasma effluents (a gas in an excited state which is exiting aplasma) which participate in a reaction to either remove material fromor deposit material on a surface. “Radical-fluorine precursors” describeradical precursors which contain fluorine but may contain otherelemental constituents. The phrase “inert gas” refers to any gas whichdoes not form chemical bonds when etching or being incorporated into afilm. Exemplary inert gases include noble gases but may include othergases so long as no chemical bonds are formed when (typically) traceamounts are trapped in a film.

Having disclosed several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of thedisclosed embodiments. Additionally, a number of well-known processesand elements have not been described to avoid unnecessarily obscuringthe present embodiments. Accordingly, the above description should notbe taken as limiting the scope of the claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the claims, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the dielectric material”includes reference to one or more dielectric materials and equivalentsthereof known to those skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

1. A substrate processing chamber, the substrate processing chambercomprising: a remote plasma region, wherein the remote plasma region isconfigured to receive a fluorine-containing precursor and form a remoteplasma from the fluorine-containing precursor; a remote plasma powersupply configured to apply a remote plasma power to the remote plasmaregion and configured to form the remote plasma; a substrate processingregion; a showerhead disposed between the remote plasma region and thesubstrate processing region, wherein the substrate processing region isfluidly coupled to the remote plasma region by through-holes in theshowerhead; a pedestal configured to support a substrate; a flangeattached to the substrate processing chamber, wherein the flange forms avacuum seal with the substrate processing chamber; a viewport attachedto the flange forming a vacuum seal with the flange, wherein theviewport is optically transmissive in a near infrared spectrum; and anoptical emission spectrometer configured to receive optical radiationafter the optical radiation passes through the viewport, wherein theoptical emission spectrometer is disposed on an exterior of the viewportand the optical radiation originates from above the substrate.
 2. Thesubstrate processing chamber of claim 1 further comprising a localplasma power supply configured to form a local plasma in the substrateprocessing region, wherein the local plasma has a local plasma powerless than 10% of the remote plasma power.
 3. The substrate processingchamber of claim 1 further comprising a fiber optic cable configured toguide the optical radiation from the viewport to the optical emissionspectrometer.
 4. The substrate processing chamber of claim 1 furthercomprising an electrode proximal to the viewport, wherein the electrodeis disposed on the exterior of the viewport.
 5. The substrate processingchamber of claim 4 further comprising a plasma power supply configuredto apply a plasma power to the electrode.
 6. The substrate processingchamber of claim 4 further comprising a second electrode configured toapply a plasma power to the electrode, wherein the electrode iselectrically insulated from the second electrode.
 7. An optical emissionspectrometer assembly, the optical emission spectrometer assemblycomprising: a flange configured to attach to a substrate processingchamber, wherein the flange is configured to form a vacuum seal with thesubstrate processing chamber; a planar viewport attached to the flangeforming a vacuum seal with the flange, wherein the planar viewport isoptically transmissive in a near infrared spectrum; an electrodeproximal to the planar viewport, wherein the electrode is disposed on anexternal side of the planar viewport; an optical emission spectrometerconfigured to receive optical radiation after the optical radiationpasses through the planar viewport, wherein the optical emissionspectrometer is disposed on the external side of the planar viewport;and a plasma power supply configured to apply a plasma power to theelectrode.
 8. The optical emission spectrometer assembly of claim 7further comprising a fiber optic cable configured to guide infraredlight from the planar viewport to the optical emission spectrometer. 9.The optical emission spectrometer assembly of claim 7 wherein the plasmapower supply is configured to apply the plasma power between theelectrode and the substrate processing chamber.
 10. The optical emissionspectrometer assembly of claim 7 further comprising a second electrodeproximal to the planar viewport, wherein the electrode is electricallyinsulated from the second electrode.
 11. The optical emissionspectrometer assembly of claim 10 wherein the plasma power supply isconfigured to apply the plasma power between the electrode and thesecond electrode.